The present invention relates to a metal laminate type cylinder head gasket sandwiched between a cylinder block and a cylinder head of an engine. More specifically, the invention relates to a metal laminate type cylinder head gasket with asymmetrical bead which balances surface pressures generated on both bottom portions of a seal bead provided around a combustion chamber hole, and prevents a dent or impression due to the surface pressures from being generated on the cylinder block and cylinder head.
With accompanying higher technologies of an engine, effort has been made for enhancing a sealing capability between the cylinder block and cylinder head. For example, in the metal laminate type gasket disclosed in Patent Document 1, as shown in FIG. 4, an asymmetrical bead 35a is formed around a combustion chamber hole 31 in a base plate 35 on a cross-section passing through a combustion chamber hole 31, a tightening bolt hole 32, and a cooling water hole 33 formed in a gasket 30. A secondary plate 36 is laminated at a projecting portion side of the asymmetrical bead 35a in the base plate 35, and is folded back at the hole edge of the combustion chamber hole 31 to extend thereof to a halfway of a concave portion of the asymmetrical bead 35a for forming a wedge stopper 36a. Therefore, the metal laminate type gasket is structured in such a way that the asymmetrical bead 35a crosses over the wedge stopper 36a (increased thickness portion) and the other general portions (non-increased thickness portions).
As described above, it has been known to use the asymmetrical bead 35a having different surface pressures generated on both bottom portions of the bead. In the well-known gasket shown in FIG. 4, an inner bottom portion 35b of the asymmetrical bead is located inside the wedge stopper 36a (increased thickness portion). An outer bottom portion 35c is located at the general portion (non-increased thickness portion) other than the wedge stopper 36a. Thus, according to the asymmetrical bead 35a, even if the bead at a side of the increased thickness portion has a large radius of curvature and a small spring constant, and the bead at a side of the non-increased thickness portion has a small radius of curvature and a large spring constant, the surface pressure of the bead bottom portion at the side of the increased thickness portion becomes large due to the thickness thereof. As described in Patent Document 1, although a sealing capability can be enhanced, it is not considered to balance the surface pressures at the both bottom portions of the seal bead around the combustion chamber hole.
Patent Document 1: Japanese patent Publication No. H04-219572
A technical object of the present invention is that, in the above described asymmetrical bead, by utilizing a difference generated in the surface pressures at the both bottom portions of the bead, in relation to a folded portion of a metal plate around an edge of the combustion chamber hole, the surface pressures generated on the both bottom portions of the seal bead are balanced around the combustion chamber hole of the metal laminate type cylinder head gasket. Thus, a stable sealing capability can be obtained and it is possible to prevent an impression or dent due to a large surface pressure which is partially applied to the cylinder block and the cylinder head from being formed.
Further objects and advantages of the invention will be apparent from the following description of the invention.